Lighting systems for illuminating liquid crystal displays employing light guides with edge lit end surfaces are known. These large area lighting systems generally do not have a uniform thickness, which is undesirable in many applications, such as backlighting of liquid crystal displays (LCDs) for pagers, hand-held computers, organizers and the like. Examples of prior art light sources are described in the following patents:
U.S. Pat. No. 4,706,173 discloses a light reflecting apparatus that uses a lamp, probably a fluorescent lamp, with light impinging on a series of exterior reflective surfaces which reflect the light into an associated display. PA1 U.S. Pat. No. 4,277,817 discloses two embodiments of a wedge-shaped body with a microgroove surface for emitting light from the grooved surface. The light is introduced in a direction that is generally parallel to the grooves. PA1 U.S. Pat. No. 4,257,084 discloses a display that reflects light off an angled surface to strike a diffusing surface which has prismatic serration to extract the light. PA1 U.S. Pat. No. 4,323,951 discloses a display having generally laminar light transmissive layers, one of which has a roughened back surface whereby light will be transmitted through a front surface of the laminar unit. PA1 U.S. Pat. No. 4,528,617 discloses a light distribution apparatus that uses a transparent double wedge-shaped member having first internally reflecting surfaces to reflect a curtain of light to a second surface which has internally reflecting surfaces which reflect the light to an opposite surface for illuminating a generally rectangular area whereby to backlight an LCD display. PA1 U.S. Pat. No. 5,050,946 discloses a light pipe that has a planar front surface for back-lighting LCDs. Light is injected into the light pipe from the ends. The back surface has a series of planar portions parallel to the front surface connected by facets, which are angled so that the injected light reflects off the facets through the front surface. A reflector having a planar, highly reflective, highly scattering surface or a sawtoothed or grooved reflecting surface is placed adjacent to facets. PA1 U.S. Pat. No. 5,126,882 discloses a light pipe in which light emitted from a surface strikes a prism member which causes the light to be directed in a predetermined direction.